J/ApJ/812/158ivo://CDS.VizieR/J/ApJ/812/158doi:10.26093/cds/vizier.18120158CDSMcQuinn K.B.W.Skillman E.D.Dolphin A.Cannon J.M.Salzer J.J.,Rhode K.L.Adams E.A.K.Berg D.Giovanelli R.Girardi L.Haynes M.P.2017-09-05T14:34:09Z2016-03-04T12:08:39ZCDS support team

CDS, Observatoire de Strasbourg, 11 rue de l'Universite, F-67000 Strasbourg, France

cds-question@unistra.frgalaxiesvariable-starshst-photometryLeo P is a low-luminosity dwarf galaxy discovered through the blind HI Arecibo Legacy Fast ALFA survey. The HI and follow-up optical observations have shown that Leo P is a gas-rich dwarf galaxy with active star formation, an underlying older population, and an extremely low oxygen abundance. We have obtained optical imaging with the Hubble Space Telescope to two magnitudes below the red clump in order to study the evolution of Leo P. We refine the distance measurement to Leo P to be 1.62+/-0.15Mpc, based on the luminosity of the horizontal branch stars and 10 newly identified RR Lyrae candidates. This places the galaxy at the edge of the Local Group, ~0.4Mpc from Sextans B, the nearest galaxy in the NGC 3109 association of dwarf galaxies of which Leo P is clearly a member. The star responsible for ionizing the HII region is most likely an O7V or O8V spectral type, with a stellar mass >~25M_{sun}_. The presence of this star provides observational evidence that massive stars at the upper end of the initial mass function are capable of being formed at star formation rates as low as ~10^-5^M_{sun}_/yr. The best-fitting star formation history (SFH) derived from the resolved stellar populations of Leo P using the latest PARSEC models shows a relatively constant star formation rate over the lifetime of the galaxy. The modeled luminosity characteristics of Leo P at early times are consistent with low-luminosity dSph Milky Way satellites, suggesting that Leo P is what a low-mass dSph would look like if it evolved in isolation and retained its gas. Despite the very low mass of Leo P, the imprint of reionization on its SFHIs subtle at best, and consistent with being totally negligible. The isolation of Leo P, and the total quenching of star formation of Milky Way satellites of similar mass, implies that the local environment dominates the quenching of the Milky Way satellites.2015ApJ...812..158Mhttps://cdsarc.cds.unistra.fr/viz-bin/cat/J/ApJ/812/158CatalogResearchIsServedByTAP VizieR generic serviceIsServedByConesearch servicerelated-toJ/ApJ/800/51 : DUSTiNGS II. Metal-poor dusty AGB stars (Boyer+, 2015)J/AJ/147/13 : Disturbers of nearby giant galaxies (Karachentsev+, 2014)J/AJ/146/145 : ALFALFA discovery of Leo P. IV. VI photom. (McQuinn+, 2013)J/ApJS/208/9 : Intrinsic colors & temperatures of PMS stars (Pecaut+, 2013)J/AJ/145/149 : ALFALFA discovery of Leo P. II. BVR photometry (Rhode+, 2013)J/AJ/145/101 : Updated nearby galaxy catalog (Karachentsev+, 2013)J/AJ/144/134 : LITTLE THINGS survey of nearby dwarf galaxies (Hunter+, 2012)J/ApJ/756/108 : HST VI phot. of variable stars in Leo T (Clementini+, 2012)J/AJ/144/4 : Dwarf galaxies in the Local Group (McConnachie+, 2012)J/AJ/143/133 : Dwarf galaxies from the ALFALFA survey (Huang+, 2012)J/AJ/142/170 : ALFALFA survey: {alpha}.40 HI source catalog (Haynes+, 2011)J/ApJS/191/352 : Abundances in stars of MW dwarf satellites (Kirby+, 2010)J/AJ/138/1037 : Star formation in Centaurus A Group dwarfs (Cote+ 2009)J/MNRAS/380/281 : Faint galactic satellites spectrosc. survey (Martin+, 2007)J/AJ/128/2170 : H{alpha} imaging of irregular galaxies (Hunter+, 2004)https://cds.unistra.fr/vizier-org/licences_vizier.htmlhttps://vizier.cds.unistra.fr/viz-bin/VizieR-2?-source=J/ApJ/812/158https://vizier.iucaa.in/viz-bin/VizieR-2?-source=J/ApJ/812/158http://vizieridia.saao.ac.za/viz-bin/VizieR-2?-source=J/ApJ/812/158https://vizier.cds.unistra.fr/viz-bin/votable?-source=J/ApJ/812/158https://vizier.iucaa.in/viz-bin/votable?-source=J/ApJ/812/158http://vizieridia.saao.ac.za/viz-bin/votable?-source=J/ApJ/812/158GETtext/xml+votablehttps://tapvizier.cds.unistra.fr/TAPVizieR/tapCone search capability for table J/ApJ/812/158/table3 (Summary of RR Lyrae Candidates in Leo P)https://vizier.cds.unistra.fr/viz-bin/conesearch/J/ApJ/812/158/table3?https://vizier.iucaa.in/viz-bin/conesearch/J/ApJ/812/158/table3?http://vizieridia.saao.ac.za/viz-bin/conesearch/J/ApJ/812/158/table3?GETtext/xml+votable180.050000true155.4349518.085452780.0055555555555555566/44332.3657755224268815e-19 4.369938604086476e-19https://cdsarc.cds.unistra.fr/viz-bin/moc/J/ApJ/812/158?format=asciidefaultJ/ApJ/812/158/table2Photometry of RR Lyrae CandidatesrecnoRecord number assigned by the VizieR team. Should Not be used for identification.meta.recordintSeq[1/10] Identification number of starmeta.numberintMJDModified Julian Date of photometric epochdtime.epochdoublemag[25.4/27.7] Photometric magnitude in Filtermagphot.magfloate_mag[0.05/0.3] Uncertainty in magmagstat.error;phot.magfloatFiltHST/ACS filter for photometric measurement (F475W (g) or F814W (I))meta.notecharJ/ApJ/812/158/table3Summary of RR Lyrae Candidates in Leo PLCLight curvesmeta.ref.urlcharPer[0.3/0.7] Mean perioddtime.period;stat.meanfloate_Per[0.01/0.2] Uncertainty in Perdstat.errorfloatrecnoRecord number assigned by the VizieR team. Should Not be used for identification.meta.recordintSeq[1/10] Identification number of starmeta.numberintRAJ2000[10] Hour of Right Ascension (J2000)pos.eq.ra;meta.mainDEJ2000[18] Degree of Declination (J2000)pos.eq.dec;meta.mainF475Wmag[26.8/27] HST/ACS F475W (g) band mean magnitude (1)magphot.mag;em.opt.Bfloate_F475Wmag[0.06/0.2] Uncertainty in F475magmagstat.errorfloatF814Wmag[26/26.3] HST/ACS F814W (I) band mean magnitude (1)magphot.mag;em.opt.Ifloate_F814Wmag[0.05/0.07] Uncertainty in F814magmagstat.errorfloatVmag[26.5/26.7] V band mean magnitude (1)magphot.mag;em.opt.Vfloate_Vmag[0.09/0.2] Uncertainty in Vmagmagstat.error;phot.mag;em.opt.VfloatNpNumber of photometric measures for this starmeta.numberintnullableSimbadSimbad column added by the CDSmeta.ref.urlcharJ/ApJ/812/158/table5Cumulative star formation history (SFH) of Leo PrecnoRecord number assigned by the VizieR team. Should Not be used for identification.meta.recordintlogt[6.6/10.1] Log timelog(yr)time.agefloatmass[0.1/1] Percent of mass formed prior to logtstat.valuefloatE_mass[0/0.5] Upper uncertainty on massstat.error;stat.maxfloate_mass[0/0.3] Lower uncertainty on massstat.error;phys.massfloat